1. Field of the Invention
The present invention relates generally to mattress constructions and, more particularly, to a unitary mattress assembly for use in bedding having an innerspring construction wherein springs of differing compressive strength are used to provide a mattress surface with a plurality of regions of different firmness.
2. Description of the Prior Art
A standard bed construction which has been popular for some time includes a frame for supporting a box spring. The box spring, in turn, is designed to support a mattress. Mattresses are available in a variety of sizes and are also constructed in various ways. One such construction which has proved to be highly desirable includes the use of an innerspring comprising a plurality of discrete coil springs encapsulated in individual fabric pockets joined together in a string. An assembly of this type is known as Marshall construction and is disclosed, for example, in U.S. Pat. No. 4,234,983, issued to Stumpf and assigned to the common assignee herein, the disclosure of which is expressly incorporated herein by reference. Pocketed strings of coils can be readily manufactured by apparatus disclosed, for example, in U.S. Pat. No. 4,401,501 also issued to Stumpf and assigned to the common assignee herein, the disclosure of which is likewise incorporated herein by reference. In essence, the latter patent teaches producing a string of pocketed coil springs by inserting the coils into spring pockets formed by ultrasonic welding of a tube of appropriate heat sensitive fabric. Once the strings of coils are formed, they may be arranged in any desired fashion such as a chevron or other pattern to provide an innerspring assembly in which the individual springs all have longitudinal axes oriented parallel one to another and the springs are closely packed together in an array having a generally rectangular shape in plan with the ends of the springs lying in a common plane. A suitable quilted foam pad of preselected thickness may then be used to cover the innerspring and provide a generally planar surface on which a person can sleep. Preferably, the innerspring is covered on both sides and has fabric edging connecting the opposed surface covers, thereby defining a unitary mattress assembly.
Mattresses of the foregoing type are generally available with differing degrees of firmness to suit the particular preference of the user. However, known unitary mattresses which are sized for two people, such as full, queen or king size mattresses, have heretofore had only one degree of firmness common to both sides of the mattress. This construction requires one user to compromise his or her preference as to firmness if another user has a different preference. To provide a bed for two people having dual firmness, it is known to construct a continuous border defining a central cavity into which two separate core mattresses are inserted, thereby providing for different degrees of mattress firmness to suit the individual preferences of two users. Such a bed construction is shown, for example, in U.S. Pat. No. 4,449,261 issued to Magnusson and assigned to the common assignee herein. However, a disadvantage of such a bed construction is that there are discernable gaps or cracks defined between the border and the mattresses inserted therewithin, as well as between the dual mattress cores themselves, which can be uncomfortable and/or inconvenient for the users. Moreover, this type of bed construction is somewhat complicated and expensive in manufacture.
Accordingly, it is desirable to provide a unitary mattress assembly having selectively positioned, multiple firmness regions therein without requiring a construction involving separate mattress cores. It is further desirable to provide a unitary mattress assembly having multiple, preferably dual firmness which can be manufactured at a cost comparable to conventional single firmness mattresses.